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By saipan59
#26720
This is a Geiger counter that I just built, mounted in the case of a cheap transistor radio. The oblong thing along the bottom is a Geiger-Mueller tube, which is a detector for "ionizing radiation", such as Beta and Gamma rays.
The small SMT board is one of my 'stackable' boards that I made a couple of months ago. It has a PIC18F2620 on it (way overkill for this project).
Just below the battery and to the left of the switch is an LED that blinks each time a particle is detected.
The large board is primarily a circuit for generating very high voltages (over 700 volts) at very low currents, necessary for the Geiger tube.
The PIC drives the voltage-booster using PPM (pulse-position modulation, similar to PWM). A small version of the output voltage goes back to a PIC A/D input, so it can actively regulate the output voltage (just like a switching power supply). A pulse from the G-M tube triggers an interrupt on the PIC, and it then blinks the LED. Note that the PIC could easily be used to measure "counts per minute" and such.

When operating, I get one count every few seconds, due to background radiation and cosmic rays and such. I also have an old wristwatch with a radium dial that outputs *many* counts per second when I hold it less than an inch or so from the tube.

Pete
Image
By saipan59
#26731
There is a PIC-based Geiger counter project in the current issue of EPE
Thanks Leon.
Do you know which G-M tube they used? I'm guessing it's a modern variety from LND or some such.
Mine uses a military surplus JAN-7616. It's 'moderately' sensitive, and quite small, and costs about half as much as a new LND 710 or whatever.

Pete
By saipan59
#26732
Here's a link to the schematic to go with the picture above:
www.geocities.com/saipan59/geiger/geiger7616_sch.jpg
The PIC board is not shown, but there's nothing interesting there - it's just 2 outputs and 2 inputs from the PIC.

The SW in the PIC is currently very simple:
1) Main Loop:
2) Do an A/D reading on AN8.
3) If the voltage is below a certain value, then output a pulse on RB4 (the pulse is always the same width, a dozen or so uS).
4) Repeat main loop.
Interrupt handler:
5) If falling-edge on RB0/INT0, then output a 1 mS pulse on RB3.

In step 3, the 'certain value' determines the output V of the boost circuit, which is set to 760V for a 7616 tube.

Pete
User avatar
By leon_heller
#26734
saipan59 wrote:
There is a PIC-based Geiger counter project in the current issue of EPE
Thanks Leon.
Do you know which G-M tube they used? I'm guessing it's a modern variety from LND or some such.
Mine uses a military surplus JAN-7616. It's 'moderately' sensitive, and quite small, and costs about half as much as a new LND 710 or whatever.

Pete
No, I noticed the project on the front page of the mag in the newsagent but didn't buy it.

Leon
By riden
#26736
Thanks for sharing your project.

To answer your question, the project in the February 2007 Everyday Practical Electronics issue uses a 18F2455/2550 with a LND712 or ZP1401 500v GM tube. It features a LCD display and USB communications to a PC client.
By nick26
#83466
I've been looking to make a similar detector and had a look at all the hits google gave, but am looking to see how small and low power I can make it. Most of the circuits I've found use the large audio transformers/inductors. Does anyone have suggestions for shrinking the magnetics or the calcs used to design a flyback converter from scratch?

Cheers in advance.
By riden
#83470
Have a look at Pete's design (the first post with the pic and corresponding schematic). His design is pretty small and doesn't require a huge inductor.
By nick26
#84012
Thanks for the referal. I did have a look, but I'm looking to go even smaller. :wink: Any suggestions for decent links to flyback converter or similar boost converter calcs would be most welcome. I'm sure I could get the PIC to run the PWM/PPM as well.
By puffyfish
#84054
How do you test a Geiger counter device? where could you find radioactive sources? would a cathode ray tube tick a Geiger counter?
By waltr
#84060
Many smoke detectors use a americium-241 and is a good source of alpha particles. However, the alpha particles can not penetrate the glass on a Geiger tube. Beta and Gamma emitters are a bit harder to come by.

Maybe you can find a watch made in 1917 to 1926 that was painted with radium.

Another is just the normal background radiation, in some areas the soil, bricks and other materials may have higher detectable counts. Pitchblende is a mineral with a high Uranium content. There are other rocks and minerals so maybe a rock and mineral store would have something. Ebay has a few pieces of pitchblende (also called Uraninite) for sale.
By riden
#84081
The mantles for gas lamps used to and may still contain thorium, which is an alpha emitter and easily detectable with a Geiger counter. Do a Google on "gas mantle radioactive" for more information.
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